The present invention relates to the field of optical telecommunications networks and describes more particularly an optical telecommunications network, of metropolitan area type, comprising a ring core.
In a known manner, networks such as certain metropolitan area networks covering fairly large geographical areas and allowing the interconnection of local networks for example situated at less than 100 km from one another have a ring type architecture.
The document entitled “A scalable transparent waveband-based optical metropolitan network”, Jean-Paul FAURE et al., ECOC'2001, 30 Sep. 2001-4 Oct. 2001, ‘Postdeadline Paper’ A.1.10, Proceedings Vol. 6, discloses a metropolitan area optical telecommunications network comprising a ring core formed from an optical fibre for the transport of optical signals in which a traffic concentrator and main communication nodes are inserted. Each main communication node connects the metropolitan area network to a local network, the latter having a plurality of so-called access nodes connected to stations.
The basic function of the traffic concentrator consists of distributing, inside the metropolitan area network, modulated and wavelength-multiplexed optical signals originating from another network referred to as a backbone, and transmitting such signals to this backbone.
Each main communication node comprises a Waveband Optical Add/Drop Multiplexer. This multiplexer is capable of diverting part of the traffic from the core (selection of one or more wavebands) to a secondary ring, on which access nodes are inserted. Each access node is connected to local networks. This multiplexer is also capable of inserting traffic into the core fibre, in the direction of the concentrator (addition of one or more wavebands); whilst allowing all the wavebands of the multiplexed signals circulating in the core to pass through.
In the following text, the traffic between two metropolitan area networks connected to one and the same backbone will be referred to as “inter-network traffic”. The traffic inside one and the same metropolitan area network, that is to say the traffic of information sent by an access node and intended for another access node connected to one and the same secondary ring or to another secondary ring of the same metropolitan area network, will be referred to as “intra-network traffic”. Until now, this traffic has been considered negligible, and its management is therefore not optimised. In fact, in order to provide correct transmission of information between two access nodes of the same metropolitan area network, it is necessary to process all the traffic (intra-network traffic and inter-network traffic) within the concentrator inserted in the core fibre. This necessitates in particular: a step of demultiplexing all the optical signals circulating in the core fibre; then a step of electronic conversion and processing of all the demultiplexed signals; in order to arrive at the selection of the signals to be remultiplexed intended for the access nodes and not for the backbone.
The document FR 2 756 442 describes another example metropolitan area optical telecommunications network comprising a ring core formed from an optical fibre in which a traffic concentrator and main communication nodes are inserted. This traffic concentrator consists of an Electronic Add/Drop Multiplexer (abbreviated to EADM) which has the drawbacks mentioned above, due to the electronic conversion and processing of all the demultiplexed signals.